There are many devices which store or further process a supply of granular material in an industrial environment. Many devices, such as grain storage apparatus or pharmaceutical handling apparatus, are designed to simply direct a supply of granular material to containers for storage. Other devices, such as a variety of industrial fabricating devices, process the material to form a component therefrom. For example, a plastic injection molding machine typically accepts a supply of pelletized plastic material, melts the pellets, injects the resulting liquid plastic into a mold, and discharges a molded part after the part has formed and cooled.
The prior art with respect to devices which handle granular materials is best described by continuing the example with respect to a product-forming machine. In the past, it has been common to use an overhead hopper for feeding the granular pellets of raw material to the product-forming machines. A quantity of pellets is placed in a very large container, such as a self-contained feed hopper, positioned above and adjacent to the machine. This arrangement permits the pellets to be gravity fed continuously into the molding machine.
In this arrangement, all of the raw material in the overhead storage container is directed to the molding machine. Frequently, the supply of raw material includes unwanted microscopic foreign metal material or foreign metal bodies, in the form of metal fragments, screws, washers, or the like. Such unwanted metallic foreign contaminants are referred to as “tramp metals” in the industry. These contaminants may be found in the plastic materials as it comes from the manufacturer due to wear or flaws in the manufacturer's transportation, manufacturing, packaging or conveying machinery. Other metal contaminants may be introduced into the raw materials from operations associated with handling the material at the end manufacturing facility itself. In addition, the growing use of recycled plastic materials for molding purposes increases the frequency of contaminant occurrences in the raw material supplies. The process of reclaiming the recyclable plastics often results in unwanted metallic contaminants becoming intermixed with the recovered plastics as a result of poor separation techniques at material recycling facilities. Frequently, recycling houses process recyclable plastics by chopping them into pieces of suitable size for reuse in molding apparatus. These plastic pieces may contain minute metal contaminants, as well as imbedded metal brackets, screws, nuts, and so on.
The presence of these metallic contaminants in the raw materials being processed in product-forming machines is undesirable for a variety of reasons. Contaminants may actually damage an industrial machine or render the finished part unusable. Even if the part is properly formed, the customer may object to the presence of metal therein as it may cause unacceptable structural, visual, or magnetic aberrations in the finished part.
Magnetic separators have been installed at the feed side of such industrial processing equipment to ensure that metallic contaminants are removed. A magnetic separator typically comprises a housing component which acts as an intermediate hopper adapted to be placed above the forming machinery for the infeed of raw materials. A plurality of magnets form a magnetic drawer adapted to be removably inserted and secured in place in the feed path of this housing. As the granular material feeds through the housing, the metallic particles are attracted to the magnets. Periodically, the drawer is removed and the metallic materials are physically cleared from the magnets. The drawer is then reinserted into the housing for additional service.
A typical device found in the prior art is found in U.S. Pat. No. 5,188,239, issued to Michael Stowe, as shown in FIG. 1. This separator system 10 utilizes a plurality of magnetic tubes 12 secured to a drawer plate 14, with the plurality of magnetic tubes 12 then being inserted into a drawer frame 16 having an outer face plate 18 which defines a plurality of openings 20. Each of the openings is provided with a casket or “wiper,” such as an o-ring, and the drawer plate 14 is configured to be movable in relation to the outer face plate 18 of the drawer frame 16, thereby allowing particulate material which has been attracted to the surface of the magnetic tubes 12 to be wiped away for cleaning purposes. During use, the magnetic tubes 12, the drawer plate 14, and the drawer frame 16 are installed as a unit within a housing 22, through a side opening 24, and raw materials are passed through the housing to remove magnetic materials using the magnetic tubes 12. The magnetic tubes 12, the drawer plate 14, and the drawer frame 16 are removed as a unit for cleaning purposes at a cleaning location.
While the prior art mechanisms have been very effective in providing reliable tramp metal separation, they suffer from some drawbacks. First, during the cleaning process, the magnetic drawer assembly must be removed from a housing into which the granular product flows. To ensure that no contaminates remain in the product stream during this process, it is essential that the product flow be interrupted during the cleaning process.
Further, removal of the drawer assembly from the housing leaves an opening in the housing through which any flow of particulate material could result in spillage of material or the ejection of dust associated with the material into the industrial environment.
It is preferable, therefore, to configure a cleaning mechanism which ensures that the magnetic separation operation continues while the magnet assemblies are being cleaned. It is also important that the cleaning operation does not require that the housing in which the magnetic separators are positioned remains closed or sealed during the cleaning operation. The present invention addresses both of these problems.